Extensive reserves of petroleum in the form of so-called "heavy crudes" exist in a number of countries, including Western Canada, Venezuela, Russia, the United States and elsewhere. Many of these reserves are located in relatively inaccessible geographic regions. The United Nations Institute For Training And Research (UNITAR) has defined heavy crudes as those having an API gravity of less than 20, suggesting a high content of polynuclear compounds and a relatively low hydrogen content. The term "heavy crude", whenever used in this specification, means a crude having an API gravity of less than 20. In addition to a high specific gravity, heavy crudes in general have other properties in common, including a high content of metals, nitrogen, sulfur and oxygen, and a high Conradson Carbon Residue (CCR). The heavy crudes generally are not fluid at ambient temperatures and do not meet local specifications for pipelineability. It has been proposed that such crudes resulted from microbial action which consumed alkanes, leaving behind the heavier, more complex structures which are now present.
A typical heavy crude oil is that recovered from the tar sands deposits in the Cold Lake region of Alberta in northwestern Canada. The composition and boiling range properties of a Cold Lake crude (as given by V. N. Venketesan and W. R. Shu, J. Canad. Petr. Tech., page 66, July-August 1986) is shown in Table A. A topped Mexican heavy crude is included for comparison. The similarities are evident.
TABLE A ______________________________________ Analysis of Maya 650.degree. F. and Cold Lake Oil Cold Lake (Lower Grand Rapids Primary Maya 650.degree. F..sup.+ Production) ______________________________________ % C 84.0 83.8 H 10.4 10.3 N 0.06 0.44 O 0.97 0.81 S 4.7 4.65 CCR 17.3 12.3 % C.sub.7 -Insoluble 18.5 15.0 Asphaltenes Ni, ppm 78 74 V, ppm 372 175 Boiling Range 75-400.degree. F. 0.62 75-400.degree. F. 1.3 400-800.degree. F. 21.7 400-650.degree. F. 15.2 800-1050.degree. F. 19.0 650-1000.degree. F. 29.7 1050.degree. F..sup.+ 58.71 1000.degree. F..sup.+ 53.8 ______________________________________
Cold Lake crude does not meet local (Canadian) pipeline specifications. A sample, believed typical, had the temperature-flow behavior shown in Table B.
TABLE B ______________________________________ Temperature Viscosity, cs (centistokes) ______________________________________ 2.degree. C. (28.degree. F.) Solid 38.degree. C. (100.degree. F.) 4797 54.degree. C. (130.degree. F.) 1137 100.degree. C. (212.degree. F.) 82 ______________________________________
The heavy crudes play little or no role in present-day petroleum refineries. Two principal reasons for this are that they are not amenable to ordinary pipeline transportation, and that because of the high metals and CCR values, they are not readily converted to a high yield of gasoline and/or distillate fuels with conventional processing. The progressive depletion and rising cost of high quality crudes, however, create a need for new technology which would inexpensively convert heavy crudes to pipelineable syncrudes, preferably with concomitant upgrading of quality, i.e. ease of conversion to the gasoline and/or distillate fuels which are in heavy demand. Such technology would augment the supply of available crude, and would make it possible for refiners to blend such syncrude with a more conventional feed for catalytic cracking and hydrocracking.
A number of methods have been proposed for decreasing the viscosity of a heavy crude oil so as to improve its pumpability. These include diluting with a light hydrocarbon stream, transporting by heated pipeline, and using various on-site processing options including visbreaking, coking and deasphalting. With most heavy crudes, conventional visbreaking or conventional deasphalting alone cannot give sufficient viscosity reduction. Attempts to reduce the viscosity to the required level by these routes usually lead to an incompatible two-phase product from visbreaking and to a very low yield of deasphalted syncrude from deasphalting. Promising alternatives for on-site production of pipelineable syncrude by combination of a thermal step and deasphalting are being proposed. Such combinations are described, e.g. in copending application Ser. No. 375,070, Ser. No. 375,066, and Ser. No. 375,068, filed on even date herewith.
Another problem usually associated with development of heavy crude oil production is the provision of roads essential to provide mobility for personnel in the oil field itself and between the oil field and adjacent housing and other support facilities. Because heavy oil fields often are located in remote areas, materials for road construction would have to be transported at high cost. Paving asphalt derived from the heavy crude oil would provide an ideal and abundant low-cost material for such road construction.
It is known that "thermal asphalts", i.e. asphalts obtained from crude oils after subjecting the oil to a temperature of 750.degree. F. or higher, as in visbreaking, produces a degraded asphalt product that is not suitable for roads.